The last of the public funerals are held for the victims of the Dec. 14 shootings in Connecticut.

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The last of the public funerals are held for the victims of the Dec. 14 shootings in Connecticut.

Dec. 22, 2012 Robbie Parker, left, carries daughter Madeline, 4, and Alissa Parker carries daughter Samantha, 3, as they leave the funeral for their other daughter, Emilie Parker, in Ogden, Utah. Parker was one of 20 children killed in the Dec. 14 shootings in Newtown.George Frey/Reuters

NEWTOWN, CONN. — State police officials said Thursday that it will take months to determine why Adam Lanza massacred students and staff at Sandy Hook Elementary School, as investigators struggle to assess his mental state prior to the shootings.

In the initial hours after the killing spree one week ago, investigators said they had uncovered “good evidence” that would provide clues into what prompted Lanza’s rampage.

But since then, police officials have become more guarded, bracing the public for a lengthy investigation that will stretch well into the new year. The extended investigation means Lanza’s motive may not be known before President Obama’s push for new gun control regulations.

Investigators are struggling to uncover clues in the case as relatives of the victims are burying the dead, which include the shooter’s mother. On Thursday afternoon, 25 relatives gathered in New Hampshire to remember Nancy Lanza, who was shot multiple times in the head by her son before he killed 26 people, and then took his own life, at the elementary school.

Donald W. Briggs, chief of the Kingston Police Department in Nancy Lanza’s hometown in New Hampshire, said the family will determine at a later date where to place her cremated remains.

Adam Lanza’s body remains in the custody of the Connecticut Medical Examiner’s Office, as officials piece together the final weeks of his life.

“At some later date, there will be information about him,” Briggs said.

Investigators’ initial optimism for quickly identifying a motive in the case dimmed as it became apparent that Lanza had been reclusive, leaving few witnesses who knew him well.

Police also are trying to recover information from a computer hard drive that was found smashed in the home he shared with his mother.

“We don’t have any smoking gun to say this is why it occurred, at least not yet,” said J. Paul Vance, a Connecticut State Police spokesman. “We are moving forward and working with our partners, and as you can assume with multiple deaths, we are looking at several months before we really have our arms wrapped around this.”

Attorney General Eric H. Holder Jr. traveled to Newtown on Thursday to meet with first responders and law enforcement officials. Officials declined to characterize the nature of the meetings.

Holder’s visit comes as the Obama administration frames its response to the Dec. 14 shootings, including pushing for new gun-control measures next year.

Before visiting Newtown, Holder attended a meeting with Vice President Biden and other senior administration officials to begin developing proposals that Obama plans to submit to Congress as early as next month.

“The president is absolutely committed to keeping his promise that we will act,” said Biden, who is heading the working group. He said that Obama will push for a ban on assault weapons and added, “We have to have a comprehensive way in which to respond to the mass murder of our children that we saw in Connecticut.”

House Speaker John A. Boehner (R-Ohio) promised Thursday to “take under advisement” any suggestions to curb gun violence put forward by the Biden commission.

“When the vice president’s recommendations come forward, we’ll certainly take them into consideration,” Boehner told reporters. “At this point, our hearts and souls ought to be thinking about those victims” of the school shooting.

Holder visited Newtown on the same day that funerals caused gridlock on city streets. With hundreds of mourners arriving for viewings, local officials have said that managing the funerals is their top priority.

Police officers from across Connecticut are in town to direct traffic and provide security at funerals and makeshift memorials. On Wednesday, a local state representative asked the media to “please leave” Newtown because “the story is over,” underscoring the community’s growing frustration at the public spotlight.

Investigators have not released any information publicly about the case since Sunday, and Sen. Richard Blumenthal (D-Conn.) said police are not likely to make any disclosures until all the funerals have been held.

But some new details about Lanza and the investigation are trickling out, most of which suggest that police have been hampered in their efforts to establish a clear motive.

A friend of Nancy Lanza’s told the Connecticut Post that Adam Lanza dreamed of becoming a Marine. His mother nixed the idea, fearing a son who didn’t like to be touched would be a poor fit for the armed forces, the friend said.

The Hartford Courant also reported Thursday that investigators believe Lanza’s computer hard drive may be “worthless” because he attempted to destroy it before he went on his shooting spree. The newspaper also reported that investigators have discovered that Lanza made few calls from his cellphone in the weeks leading up to the incident.

But Vance said investigators remain confident that they can still recover clues from the damaged hard drive.

With Lanza reportedly obsessed with video games, Vance said “all electronics” from his house are in police custody.

“State police have a very comprehensive crime laboratory, and the FBI has the same capability,” Vance said. “Any electronic equipment that was seized is going to be examined, and we are certainly believing there is information that is going to be helpful to us in this case.”

Vance said investigators will work through the holidays “dissecting the shooter from the day he was born to the day he died.”

“We spent countless hours going through every stitch of that house we could uncover,” Vance said.

Rep. Joe Courtney (D-Conn.) said “the hunger for information” about the Lanza family and Adam Lanza’s motive is “overwhelming” around the state.

But Courtney, a former public defender who represents eastern Connecticut, said elected officials and residents remain confident that police and federal officials are working as fast as they can, “given the fact some of the key witnesses lost their lives.”

“I have some understanding how difficult it is to piece something like this together,” Courtney said. “They want to be careful about not making bad conclusions. . . . This is about as large as it gets, so I still give them some slack and time.”

Tim Craig is The Post’s bureau chief in Pakistan. He has also covered conflicts in Iraq, Afghanistan and within the District of Columbia government.

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